Crystal growth and morphology evolution of D88 (Mn, Fe)5Si3 phase and its influence on the mechanical and wear properties of brasses

The crystal growth and morphology evolution of D88 transition metal silicide and its influence on the mechanical properties of alloys have yet to be determined. In this paper, the effect of in situ-formed D88 (Mn, Fe)5Si3 phase on the mechanical and wear performances of brasses is presented. By means of deep etching and phase extraction technologies, the morphology of (Mn, Fe)5Si3 phase is found to exhibit long hexagonal prism, due to the higher growth velocity in the <0001> direction than that of <11 2̅ 0> according to the Mn-Si bond chain arrangement. Two kinds of hollows, i.e. internal hollow and prism facet hollow, are formed on the coarse primary (Mn, Fe)5Si3 prisms, which can be ascribed to the restrained solute diffusion within the prism and attachment limited kinetics on the prism facet, respectively. With increasing the (Mn, Fe)5Si3 content, the hardness and yield strength increase effectively, which mainly results from the load transferring effect and grain refinement, supported by the good agreement between calculated and experimental results. The fracture mode transforms from ductile failure to quasi-cleavage and cleavage failure. Severe cracking tendency of high aspect ratio primary (Mn, Fe)5Si3 particles containing large-sized hollows leads to slight increment in ultimate tensile strength and great ductility decrease at high (Mn, Fe)5Si3 content. In addition, the fine eutectic (Mn, Fe)5Si3 particles are beneficial to improve the ductility by acting as effective barriers to crack cleavage and void growth. The proper combination of thinner primary and eutectic (Mn, Fe)5Si3 particles is found to efficiently restrain the crack creation and result in a good wear resistance. This study may be helpful to design high performance alloys reinforced with transition metal silicides by tailoring their morphology.